Through the years, chlorinated solvents have had a large impact on several industries, including pharmaceuticals, chemical processing, food extraction, dry cleaning, and metal cleaning. With wide spread use and improper handling and storage, extensive soil and water damage has occurred. Due to their toxicity, carcinogenicity, and persistence in the environment, chlorinated solvents are listed by the United States Environmental Protection Agency as high priority pollutants. If left untreated, chlorinated solvents may remain unchanged for a period of fifty years or more. The most common chlorinated solvents used are methylene chloride, tetrachloroethene, trichloroethene, carbon tetrachloride, chloroform, tetrachloroethane, dichloroethene and vinyl chloride. Carbon tetrachloride is a systematic poison of the nervous system, the intestinal tract, the liver, and the kidneys. Vinyl chloride and methylene chloride are known carcinogens, and could also affect the nervous system, the respiratory system, the liver, the blood, and the lymph system.
Chlorinated solvents are often found in separate phases mixtures commonly referred to as dense nonaqueous-phase liquids (“DNAPLs”). DNAPLs are visible, denser-than-water, separate oily phase materials in the subsurface whose migration is governed by gravity, buoyancy, and capillary forces. Chlorinated solvents partition into the water phase to create a dissolved contaminant plume when in contact with water, thus creating a long-term, continuing source of contamination as the soluble constituents slowly dissolve into moving groundwater.
One common technique for treating contaminated matter is the “pump-and-treat” method in which contaminated groundwater is pumped to the surface, cleaned chemically or by passing the groundwater through a bioreactor, and then reinjected into the groundwater. This process is carried out over a long period and various factors complicate the removal of these contaminants from the environment. Also, they are very volatile, highly mobile, denser than water, and generally found in the environment as mixtures of products with different degrees of chlorination. The “pump-and-treat” method is therefore problematic.
The problems with the “pump-and-treat” method can be overcome with the use of anaerobic microorganisms which have the capability to decompose a wide range of highly chlorinated compounds. However, anaerobic microorganisms are at a disadvantage in that their growth is slow when compared to that of aerobic organisms. In-situ they are at an even greater disadvantage due to the partitioning of the targeted substrates into the soil matrix. There is therefore a need in the art to utilize the ability of anaerobic microorganisms to decompose chlorinated compounds which can be achieved at a faster rate.